The present invention relates to systems and methods for producing a flow of preferred-spin-polarization-direction electrons, and more particularly is an optically pumped direct extraction electron spin filter system and method of utilizing a predominately single handedness, preferably laser system produced, beam of photons to optically pump electrons in atoms, (typically alkali atoms), to a dark-ground state therewithin, in a preferred-spin-polarization direction. Said method is practiced in the presence of a magnetic field which is oriented essentially co-linear with said beam of photons and said system and method serve to, in a below atmospheric pressure ambient, convert a multiplicity of typically internal electric discharge generated, xe2x80x9crandom-spinxe2x80x9d electrons into a multiplicity of directly extracted preferred-spin-polarization-direction electrons via pumped dark-ground state atomxe2x80x94electron collision mediated exchange mechanism(s). Said system preferably comprises a single chamber essentially enclosed space and the presence of helium in an electron polarization direction enhancing xe2x80x9cbuffer gasxe2x80x9d contained therewithin.
As described in a book by J. Kessler, titled xe2x80x9cPolarized Electronsxe2x80x9d, 2nd Ed. (Springer, Berlin 1985), while the production of electrons with a preferred-spin-polarization-direction for use as a probe of spin-dependent phenomena is known, electrons with a preferred-spin-polarization-direction are difficult to produce. Further references which document that polarized electrons are an indispensable probe of spin-dependent phenomena in many areas of physics include xe2x80x9cPolarized Electrons In Surface Physicsxe2x80x9d Edited by R. Feder, (World Scientific, Singapore, 1985); and xe2x80x9cPolarized Gas Targets And Polarized Beamsxe2x80x9d, (Seventh International Workshop), Edited by Holt and Miller, AIP Conference Proceedings Series CP421, (AIP New York 1998). Note, the above identified references are incorporated herein by reference to provide general background.
Continuing, the development of sources of polarized electrons began with Bohr""s rejection of magnetic spin filters as described in xe2x80x9cThe Scattering Of Fast Electrons By Atomic Nucleixe2x80x9d Mott, Proc. R. Soc., London, Ser. A 124, 425 (1929) and xe2x80x9cStern-Gerlach Effect For Electron Beamsxe2x80x9d, Batelaan, Gay, Schwendiman, Phys. Rev. Lett. 79, 4517 (1997). The use of Mott scattering to produce small currents of polarized electrons is discussed in xe2x80x9cElectron Polarizationxe2x80x9d, Shull et al., Phys. Rev. 63, 29 (1943) and in xe2x80x9cA Method Of Measuring The Gyromagnetic Ratio Of The Free Electronxe2x80x9d, Louisell et al., Phys. Rev. 91, 475 (1953).
As described in the previously cited Holt and Miller reference titled xe2x80x9cPolarized Gas Targets And Polarized Beamsxe2x80x9d, the best of said polarized electron spin sources can produce high currents, (eg. microamps), and polarizations approaching unity, where Polarization (P) is defined as:
P=(N+xe2x88x92Nxe2x88x92)/(N++Nxe2x88x92) 
where N+(xe2x88x92) represent the number of electrons with xe2x80x9cupxe2x80x9d and xe2x80x9cdownxe2x80x9d spins, respectively.
Said Holt and Miller reference also discloses that state-of-the-art polarized electron sources use either photoemission from negative-affinity GaAs, (or variants of the GaAs basic structure), or chemi-ionization of optically pumped metastable He (He*); and that both techniques can produce electron polarizations in excess of seventy (70%) at current levels of several hundred microampers. As described in xe2x80x9cA source Of Highly Spin-Polarised Slow Electrons Based On The xe2x80x98Fano Effectxe2x80x99 On Caesium Atomsxe2x80x9d, Mollenkamp et al., J. Phys. E 15, 692, (1982), it is noted that earlier polarized electron sources which utilized, for instance, the xe2x80x9cFano Effectxe2x80x9d, produced currents which were four orders of magnitude lower, with at best a similar polarization, and with much larger beam emittance.
Unfortunately, GaAs and H* sources are technically complex and pose difficulties in operation. GaAs sources must be operated under ultrahigh vacuum/low contamination conditions, produce only picoamp current levels, and production of a negative electron affinity photocathode is currently technically difficult, as described in xe2x80x9cGaAs Spin Polarized Electron Sourcexe2x80x9d, Pierce et al., Rev. Sci. Instrum. 51, 478 (1980) and the previously cited Holt and Miller reference. Helium H* sources are easier to operate, but are large, mechanically complex, and require high-throughput vacuum pumps to achieve optimum performance. Helium H* sources are described in xe2x80x9cImproved Source Of Polarized Electrons Based On A Flowing Helium Afterglowxe2x80x9d, Rutherford et al., Rev. Sci. Instrum. 61, 1460 (1990), and in xe2x80x9cThe Orsay Polarized Electron Source From A Flowing Helium Afterglowxe2x80x9d, Arianer et al., Nucl. Instrum. Meth. A 382, 371 (1996).
Work by McCusker et al., reported in an article titled xe2x80x9cCumulative Ionization In Optically Pumped Helium Discharges: A Source Of Polarized Electronsxe2x80x9d, Phys. Rev. A 5, 177 (1972), resulted in provided a He* source in which electrons are extracted directly from a discharge instead of being produced by chemi-ionization in a flowing discharge afterglow. While the design of system which utilizes chemi-ionization in a flowing discharge afterglow is more complex than systems which utilize direct extraction, systems which utilize flowing discharge afterglow produce much higher currents and electron polarizations.
As alluded to, systems that utilize direct extraction are inherently less complex that are systems which utilize flowing discharge afterglow and therefore offer utility. However, efforts by the inventors herein to develop an improved direct extraction source have met with limited success. The reason for the low polarization achieved from the direct extraction source investigated by the inventors herein is believed to be that unpolarized electrons are produced by ionization of ground state atoms, which effect competes with polarized electron production by exchange collisions and associated ionization involving spin-polarized metastable atoms. The problem with direct extraction is that it relies on the existence of a discharge with a relatively high ratio of metastable atoms to ground state atoms. The flowing afterglow approach overcomes this problem, but involves, as a trade-off, greater cost and complexity.
At this point it is disclosed that the present invention is based in the insight that if the key-electron-polarizing collisions mechanism involved ground-state atoms, instead of excited atoms, the problem of unpolarized electrons being produced by ionization of ground state atoms, would be overcome. The present invention then provides that free electrons diffuse under the action of an electric field through Rb vapor that has been spin polarized by optical pumping, and through spin-polarizing xe2x80x9celectron-exchange-mechanismxe2x80x9d collisions with the Rb, the free electrons become spin-polarized and are directly extracted as a beam.
Continuing, the idea of utilizing spin-exchange collisions to polarize ensembles of electrons is not new. Articles by:
Fargo et al., titled xe2x80x9cThe Production Of Polarized Electron Beams by Spin Exchange Collisionxe2x80x9d, Phys. Lett. 20, 279 (1966) and xe2x80x9cOn A Sourcve Of Polarized Electronsxe2x80x9d, Proc. R. Soc. Edinb. A, Math. 70, 15 (1971/72); and by
Krisciokaitis-Krisst et al., titled xe2x80x9cTheoretical Consideration Of Spin-Polarized Electron Source Based On Elastic Electron-Hydrogen Spin-Exchange Collisionsxe2x80x9d, Nucl. Instrum. Methods Phys. Res. (Netherlands) 83, 45 (1970); and xe2x80x9cPrototype Polarized-Electron Source Through Electron-Hydrogen Spin Exchange With Teflon Containment Of Hydrogen And A Longitudinal Magnetic Trapxe2x80x9d, Nucl. Instrum. Methods Phys. Res. (Netherlands) 118, 157 (1974);
describe use of spin-exchange collisions to polarize ensembles of electrons, Said articles describe pulsed sources of polarized electrons which operate by directing beams of polarized Rb and H through electron traps. The Rb atoms are polarized by passage through a hexapole magnet. In turn, electrons become polarized and are periodically dumped. Said procedure provides between forty (40%) and sixty (60%) polarization and 104-107 electrons per bunch at a sixty (60) Hz trap dumping rate.
It is to be appreciated, however, that a spin-filter is a more efficient electron polarizer that the trap-beam configuration because angular momentum can be transferred to the system much more rapidly by optical pumping. Moreover, the electron densities are much higher in a discharge than in a trap, thereby enabling higher current densities. It is also to be noted that as described in an article by Coulter et al., titled xe2x80x9cNeutron Polarization With A Polarized 3He Spin Filterxe2x80x9d, Nucl. Instrum. Methods Phys. Res. A, Accel. Spectrom. Detect. Assoc. Equip. (Netherlands) 288, 463, (1990), the optically-pumped spin-filter concept has been previously successfully utilized to polarize beams of cold neutrons in collisions with oriented 3He nuclei. In addition, articles by Drouhin et al. titled xe2x80x9cElectron Transmission Through Ultra-thin Metal Layers And Its Spin Dependence For magnetic Structures, J. Magn. Mat. 151, 417 (1995), and by Schonhense et al., titled xe2x80x9cTransmission Of Electrons Through Ferromagnetic Material And Applications To Detection Of Electron Spin Polarizationxe2x80x9d, Ann. Physik. (Liepzig) 2, 465, (1993) describe polarization of low current beams of electrons caused to pass through magnetized thin solid films.
Further, it is noted that non-enabling Abstracts of talks given by the inventors herein appeared in Compilations of Abstracts, one for the American Physical Society Conference, in April, Vol. 42, No. 2 (1997); and one for the Gaseous Electronics Conference, October Vol. 42, No. 8.
A search of Patents has provided very little. A Patent to Baptist et al., U.S. Pat. No. 4,835,438, however, is disclosed as it describes a source of spin-polarized electrons which involves an emissive ferromagnetic micropoint cathode in combination with a magnetic field. U.S. Pat. No. 3,968,376 to Pierce et al. is also disclosed as it describes a source of spin-polarized electrons wherein a semiconductor is irradiated with circularly polarized light. A Patent to Kishino et al., U.S. Pat. No. 5,747,862 describes a spin-polarized electron emitter comprising a semiconductor having a split valance band which can emit electrons from a surface thereof upon incidence of laser radiation. A reflecting mirror serves to effect multiple reflections between said reflecting mirror and the emitting surface. A Patent which describes isotope separation utilizing a magnetic field, a polarized light beam and an electron beam is U.S. Pat. No. 4,704,197 to Trajmar. Two Patents to Bowman, U.S. Pat. Nos. 4,976,911 and 5,063,019 describe spin polarization of 3He utilizing laser induced polarization, optionally involving an alkali-metal vapor. Said produced 3He is utilized in control of nuclear fission. Two other Patents identified during the search, and which are mentioned for that reason only are U.S. Pat. Nos. 5,504,340 and 5,617,860 to Mizumura et al and Chupp et al. Said Patents, however, are not considered relevant.
It can be concluded that prior art exists which teaches use of polarized laser beams, magnetic fields and alkali metal vapors in producing electrons with a preferred spin, however, even in view of the identified references, there remains need for an optically pumped direct extraction electron spin filter system and method for utilizing a predominately single handedness, preferably laser system produced, beam of photons to optically pump electrons into a preferred spin direction in ground state atoms in the presence of a magnetic field which is oriented essentially co-linear with said beams of photons, which system and method serve to, in a below atmospheric pressure ambient, (eg. one (1) Torr), which contains one or more buffer gas(es), which preferably comprise Helium, convert a multiplicity of, typically electric discharge generated, xe2x80x9crandom-spinxe2x80x9d electrons into a multiplicity of directly extracted preferred-spin-polarization-direction electrons via pumped ground state atomxe2x80x94electron collision mediated exchange mechanism(s).
To facilitate understanding, it is disclosed that the term xe2x80x9cElectron Spin Filterxe2x80x9d, as used herein, identifies a system which acquires a multiplicity of electrons which have no predominance of preferred-spin-polarization-direction, and provides as output, via a xe2x80x9cfilteringxe2x80x9d mechanism, a multiplicity of electrons which have a predominance of preferred-spin-polarization-direction. The basis of operation depends on electron exchange mechanisms involving polarized atoms as said multiplicity of electrons without a predominance of preferred-spin-polarization-direction are caused to pass through an enclosed space which contains said polarized atoms. In that light it is noted that the present invention bears remote similarity to the Holt and Miller polarized electron source which provides that electrons without a predominance of preferred-spin-polarization-direction be impinged upon negative electron-affinity GaAs, thereby effecting photoemission of electrons with a predominance of preferred-spin-polarization-direction from said negative-affinity GaAs; but that the present invention is dramatically different from the Krisciokaitis-Krisst et al. system which utilizes spin-exchange collisions to polarize ensembles of electrons, followed by periodic xe2x80x9cdumpingxe2x80x9d thereof. Said Krisciokaitis-Krisst et al. system provides polarized electrons in pulses by causing interaction of non-polarized electrons with beams of H and polarized Rb concurrently entered into electron traps, said Rb atoms having been polarized by passage through a hexapole magnet.
Continuing, the present invention system is an optically pumped direct extraction electron spin filter and method of producing a directly extracted flow of electrons that have a preferred-spin-polarization-direction. Said present invention system comprises an essentially enclosed space, (preferably single vacuum chamber), and further comprises vacuum pumping means for producing a below atmospheric pressure ambient in said essentially enclosed space, as well as means for creating a magnetic field therein. Additionally said present invention system comprises means for producing a beam of predominately single handedness, (electromagnetic radiation), photons which are, in use, caused to enter said essentially enclosed space along a locus which is essentially oriented co-linear with the direction of a magnetic field which is caused to exist therein by said means for creating a magnetic field in said essentially enclosed space. Said present invention system further comprises means for providing atoms to said essentially enclosed space,
which atoms have a first excited state above the ground state thereof which photons in a beam of predominately single handedness photons produced by said means for producing a beam of predominately single handedness, (electromagnetic radiation), photons can, in use, optically pump electrons thereinto by interaction therewith.
Said present invention system also comprises means for providing a buffer gas, preferably comprised of Helium, to said essentially enclosed space, which buffer gas serves to, amongst possible other effects, absorb emitted photons from excited atoms which relax back to ground state and/or act as a shield to optically pumped ground state atom interactions with internal walls of said essentially enclosed space.
Said present invention system also comprises means for providing electrons to said essentially enclosed space, (preferably by electric discharge in said buffer gas present therein), as well as a means for establishing a directly extracted flow of polarized electrons, (preferably utilizing an applied electric field), of a preferred-spin-polarization-direction, from said essentially enclosed space.
Said present invention system also comprises means for functionally interconnecting and positioning said means identified infra herein, the resulting configuration of which is generally demonstrated FIG. 1a. It is noted that said interconnection means comprise off-the-shelf available vacuum seals and structural elements.
In use, the present invention provides that a below atmospheric pressure ambient is caused to exist in said essentially enclosed space by said means for producing a below atmospheric pressure ambient in said essentially enclosed space, and that a magnetic field be caused to exist in said essentially enclosed space by said means for creating a magnetic field in said essentially enclosed space. In addition a beam of predominately single handedness photons is caused to enter said essentially enclosed space from said means for producing a beam of predominately single handedness electromagnetic radiation photons, along a locus which is essentially co-linear with the direction of said magnetic field caused to exist therein by said means for creating a magnetic field in said essentially enclosed space. Atoms which have a first excited state above the ground state thereof which photons in the beam of predominately single handedness photons produced by said means for producing a beam of predominately single handedness electromagnetic radiation photons can optically pump electrons into, are entered to said essentially enclosed space from said means for providing atoms to said essentially enclosed space. (Note that in use, said imposed magnetic field serves to maintain the preferred spin polarization of electrons in atoms which are affected by optical pumping, and causes produced polarized electron precession diameters to be small thereby allowing a greater number thereof to exit a direct access means, (eg. a hole containing flat plate or cone-shaped skimmer), in use thereby increasing yield). Buffer gas which preferably comprises Helium, (which buffer gas serves to, for instance, absorb emitted photons from optically pumped excited atoms which relax back to ground state and/or shelter pumped atoms from ground state electron spin polarization scattering interacting with internal walls of said essentially enclosed space), is entered to said essentially enclosed space via said means for providing a buffer gas to said essentially enclosed space, and electrons from said means for providing electrons to said essentially enclosed space are also created in said essentially enclosed space by an electric discharge therein.
Continuing, practice of the present invention provides that, in use, electrons in atoms caused to be present in said below atmospheric pressure ambient containing essentially enclosed space are continuously optically pumped to a dark-ground state in said atoms, with a preferred-spin-polarization. Additionally, it is to be understood that electrons entered to said essentially enclosed space by said means for providing electrons to said essentially enclosed space, interact with said optically pumped dark-ground state atoms and by pumped atomxe2x80x94electron exchange mechanism(s) are caused to be of a preferred-spin-polarization-direction, and are then caused to exit said essentially enclosed space as a flow of directly extracted polarized electrons of a preferred-spin-polarization-direction.
It is to understood that the ultimate direction of preferred electron spin is determined by the xe2x80x9cHandednessxe2x80x9d of the beam of optical pumping photons in said beam of predominately single handedness photons, and the terminology xe2x80x9cpredominately single handednessxe2x80x9d identifies a beam of electromagnetic radiation photons which is characterized by a predominance of either left or right handedness. The preferred polarization state of the beam of predominately-single-handedness-photons is ideally describable as being xe2x80x9cpartially circularly polarizedxe2x80x9d, but any functional polarization state is to be considered as within the scope of the present invention.
It is noted that the atoms which have a first excited state above the ground state thereof which photons in the beam of predominately single handedness photons can optically pump electrons into, are alkali atoms, and specifically preferred are Rhubidium (Rb) atoms. Rhubidium atoms are especially well suited for producing electrons with a preferred-spin-polarization-direction, via pumped ground state atomxe2x80x94electron exchange mechanism(s), where electrons in said Rhubidium atoms are continuously optically pumped by a beam of predominately single handedness photons into a dark-ground state in said Rhubidium atoms.
It is further noted that preferred means for producing a beam of predominately single handedness photons is a laser system, and a standing wave dye laser which is pumped by an argon laser system was utilized in experimental work by the Inventors of the present invention.
It is further noted that the terminology xe2x80x9cdark-ground statexe2x80x9d refers to electrons in polarized atoms, which electrons have in a preferred spin direction, and which are in a final pumped xe2x80x9cdarkxe2x80x9d ground state. A dark-ground state is achieved by pumping atoms with random-spin electrons therein, into excited states, followed by a relaxation of said electrons into said dark-ground state, with the condition being met that said electrons then have a preferred spin direction.
In addition, it is disclosed that the buffer glass which serves improve preferred-spin-polarization-direction electron yield preferably comprises helium, and is preferably selected from the group consisting of: (helium, and a mixture of nitrogen and helium), although rare gasses such as neon, argon and krypton etc. can also be utilized. The mechanism of Nitrogen in increasing said yield involves absorbtion of photons emitted from relaxing pumped atoms. The mechanism of Helium in increasing said yield, while not absolutely certain, is thought to be that it serves to shield optically pumped dark-ground state atoms from interacting with the internal walls of the essentially enclosed space better than does Nitrogen, rather than from a buffer of emitted photon emission effect at which Nitrogen is better. (It is noted that the Inventors of the present invention remain surprised by the unpredicted, experimentally discovered, effect of Helium).
A present invention method of producing a flow of polarized electrons with a preferred-spin-polarization-direction, comprises the step of:
A. providing an optically pumped direct extraction electron spin filter system for producing a flow of directly extracted electrons with a preferred-spin-polarization-direction as described infra herein;
and further comprises, in any functional order, the steps of:
B. establishing a below atmospheric pressure ambient in said essentially enclosed space;
C. causing a magnetic field in said essentially enclosed space;
D. producing a beam of predominately single handedness photons and causing it to enter said essentially enclosed space along a locus which is essentially co-linear with the direction of said magnetic field caused to exist in said essentially enclosed space in step C.;
E. entering atoms which have a first excited state above the ground state thereof which photons in a beam of predominately single handedness photons produced by said means for producing a beam of predominately single handedness, (electromagnetic radiation), photons can optically pump electrons thereinto by interaction therewith, to said essentially enclosed space;
(Note, that this step can be performed by constructing the essentially enclosed space so that a flexible appendage extends therefrom and opens thereinto, into which flexible appendage is placed, prior to use, a sealed ampoule containing, for instance, Rb atoms. In use such a positioned ampoule is broken by flexing said flexible appendage to release said atoms present therein into said essentially enclosed space. Use of a rigid appendage and a Rb atom containing ampoul which includes a magnetic means xe2x80x9campoul breaking meansxe2x80x9d for use in breaking said ampoul, is also within the scope of the present invention);
F. entering a buffer gas, which optionally comprises Helium, to said essentially enclosed space, which buffer gas serves to increase yield of electrons with a preferred-spin-polarization-direction;
G. causing a multiplicity of electrons to be in said essentially enclosed space;
H. causing said atoms entered in Step E. to be continuously optically pumped by photons in said beam of predominately single handedness photons entered in Step D. to the end that said atoms have electrons therein optically pumped to a dark-ground state wherein said electrons therein have a preferred-spin-polarization;
I. causing said multiplicity of electrons entered to said essentially enclosed space by said means for providing electrons to said essentially enclosed space in Step G. to interact with said optically pumped dark-ground state atoms by electron exchange mechanism(s) such that at least some of said multiplicity of electrons entered to said essentially enclosed space in Step G. are caused to be of a preferred-spin-polarization-direction; and
J. causing said electrons with a preferred-spin-polarization-direction as produced in Step I. to exit said essentially enclosed space as a directly extracted flow of polarized electrons of with preferred-spin-polarization-direction, via said means for establishing a flow of polarized electrons with a preferred-spin-polarization-direction and causing them to flow out of said essentially enclosed space.
To aide with disclosure, the following are provided as guidelines:
The step A. providing of a single chamber essentially enclosed space involves providing single vacuum chamber containing enclosed space which is typically on the order of fifteen (15) centimeters long and four (4) centimeters in diameter, (ie. between one-hundred (100) and one-thousand (1000) cubic centimeters, and nominally approximately two-hundred (200) cubic centimeters volume).
The step B. establishment of a below atmospheric pressure ambient in said essentially enclosed space involves establishing a pressure in said essentially enclosed space of One-tenth (0.1) to Thirty (30) Torr.
The step C. causing of a magnetic field in said essentially enclosed space involves establishing a magnetic field of between One-Hundred-Fifty (150) and One-thousand (1000) Gauss. (Note for comparison that the Earth""s magnetic field is one-half (0.5) Gauss). It is noted that said magnetic field, in addition to maintaining pumped atom polarization, serves to keep produced polarized electrons from precessing in relatively wide xe2x80x9ccirclesxe2x80x9d, thereby enabling enhanced yield of directly extracted electrons through a small internal diameter hole skimmer means.
The step D. producing of a beam of predominately single handedness photons and causing it to enter said essentially enclosed space along a locus which is essentially co-linear with the direction of said magnetic field caused to exist in said essentially enclosed space in step C. involves use of a standing wave dye laser which is pumped by an argon laser system. In particular a Twelve (12) Watt Coherent Innova 90 CW Argon Laser with a Five (5) Watt output with all Etalon Filters removed, and a Spectra-Physics Dye Laser, Model No. 375B which utilized Exciton LDS-751 dye were utilized. An approximately forty (40) GHz wide spectrum was achieved. It is further noted that additional research utilizing a Diode Bar Laser is being pursued.
The step E. entering of;
which atoms have a first excited state above the ground state thereof which photons in a beam of predominately single handedness photons produced by said means for producing a beam of predominately single handedness electromagnetic radiation photons can, in use, optically pump electrons thereinto by interaction therewith,
xe2x80x83to said essentially enclosed space, involves atoms which are well suited to producing dark-ground state electrons with a preferred-spin-polarization, when optically pumped by a beam of predominately single handedness photons. In particular, alkali atoms, preferably Rhubidium atoms at a concentration of between 1011 and 1014, (nominal 1012), per cubic centimeter, are well suited for this purpose.
The step F. use of a buffer gas entered to said essentially enclosed space involves buffer gas which is typically selected from the group consisting of: (helium, and a mixture of nitrogen and helium), but can comprise rare gasses such as neon, argon, krypton etc.
The step G. entering of a multiplicity of electrons to said essentially enclosed space generally involves electrons generated by an electric discharge caused to occur within said essentially enclosed space.
An alternative description of a present invention optically pumped direct extraction electron spin filter system for producing a directly extracted flow of electrons with a preferred-spin-polarization-direction provides that an elongated single vacuum chamber contained essentially enclosed space of a nominal volume on the order of one-hundred (100) to one-thousand (1000) cubic millimeters be present. Said single vacuum chamber contained essentially enclosed space, during use, is caused to contain a mixture of alkali atoms and buffer gas at a nominal pressure of between one-tenth (0.1) and thirty (30) Torr, and said single vacuum chamber contained essentially enclosed space comprising an electric discharge source of electrons therewithin and a window for allowing entry thereinto of an externally generated beam of photons of predominately single handedness, in addition to having means for extracting a flow of electrons with a preferred-spin-polarization-direction. Said single vacuum chamber contained essentially enclosed space has, during use, impressed therewithin by external means, a longitudinally directed magnetic field of at least one-hundred-fifty (150) Gauss and a longitudinally directed electric field of at least ten (10) volts/cm. During use an externally generated beam of photons of predominately single handedness is entered into said single vacuum chamber contained essentially enclosed space through said window for allowing entry thereinto of an externally generated beam of photons of predominately single handedness, the locus of said beam of photons of predominately single handedness being directed essentially co-linear with said magnetic field which is impressed therewithin by external means. Additionally, during use interaction of said beam of photons of predominately single handedness with said alkali atoms continuously causes electrons in said alkali atoms to be optically pumped to a dark-ground state in said alkali atoms, wherein said electrons have a preferred-spin-polarization-direction. Further, during use said electric discharge source of electrons within said single vacuum chamber essentially enclosed space is caused to operate and provide a multiplicity of electrons by internal electric discharge in said buffer gas. Also, during use electrons produced by said internal electric discharge in said buffer gas are caused to interact with said alkali atoms which are caused to contain dark-ground state electrons with a preferred-spin-polarization-direction to the end that, via electron exchange mechanisms, at least some of said multiplicity of electrons entered to said essentially enclosed space by said internal electric discharge are caused to be of a preferred-spin-polarization-direction. Finally, during use at least some of said resulting electrons with a preferred-spin-polarization-direction are caused to exit said vacuum chamber contained essentially enclosed space via said means for extracting a flow of electrons with a preferred-spin-polarization-direction, under the influence of said externally impressed longitudinally directed electric field. Attributes of the optically pumped direct extraction electron spin filter system for producing a directly extracted flow of electrons with a preferred-spin-polarization-direction can include at least one additional selection from the group consisting of:
a. said buffer gas comprises a rare gas such as neon and/or argon, and/or krypton etc.
b. said buffer gas comprises helium;
c. said buffer gas comprises nitrogen;
d. said buffer gas pressure in said vacuum chamber contained essentially enclosed space is during use, nominally four-tenths (0.4) Torr, (note that this can be considered a xe2x80x9cpartial pressurexe2x80x9d where the pressure in the vacuum chamber contained essentially enclosed space is greater than said four-tenths (0.4) Torr);
e. said pressure in vacuum chamber contained essentially enclosed space is during use, pumped into the range of one-tenth (0.1) to thirty (30) Torr, nominally one (1), Torr prior to entry of buffer gas;
f. said longitudinally directed magnetic field impressed within said vacuum chamber contained essentially enclosed space by said by external means is between one-hundred-fifty (150) and one-thousand (1000) Gauss;
g. said longitudinally directed electric field impressed within said vacuum chamber contained essentially enclosed space by said by external means is at least ten (10) volt/cm;
h. said externally generated beam of photons of predominately single handedness is generated by a Laser system which comprises a twelve (12) watt Coherent Innova 90 CW Argon Laser;
i. with a Five (5) Watt output with all Etalon Filters removed, and a spectra-Physics Dye Laser, Model No. 375B which utilizes Exciton LDS-751 dye resulting in photons with a nominal wavelength of seven-hundred-ninety-five nanometers;
j. below atmospheric pressure in said vacuum chamber contained essentially enclosed space is effected utilizing only a roughing pump with the capability of producing a nominal minimum pressure of a millitorr therewithin;
k. said window for allowing entry thereinto of an externally generated beam of photons of predominately single handedness further comprises a heater means which, during use, maintains the temperature thereof at a nominal one-hundred-fifty (150) degrees Centigrade to prevent alkali atom deposition thereupon.
Finally in this Section of this Disclosure, it is emphasized that the preferred embodiment of the present invention optically pumped direct extraction electron spin filter system utilizes a single vacuum chamber containing essentially enclosed space, in which all described phenomena occur. That is, multiple separate chambers are not required, or even desirable, in realization of the present invention system. In addition, while use of high or ultra-high vacuum producing pumping means, (eg. diffusion etc.), is within the scope of the present invention, it is to be appreciated that no expensive high or ultra-high vacuum pumping means for producing a below atmospheric pressure ambient in said essentially enclosed space, is required to practice the present invention. In fact, production of electrons with a predominately single polarization-spin-direction requires no more than the vacuum producing capability of a typical roughing pump which can typically provide down to a milli-torr pressure level in a single vacuum chamber which is typically on the order of fifteen (15) centimeters long and four (4) centimeters in diameter, (ie. between one-hundred (100) and one-thousand (1000) cubic centimeters, and nominally approximately two-hundred (200)cubic centimeters volume). While it is admittedly necessary to provide very much lower pressures, (eg. 10xe2x88x928 Torr), in follow-on systems which-utilize-electrons with a predominately single polarization-spin-direction that are produced by the operation of the present invention optically pumped direct extraction electron spin filter system, said polarized electron utilizing systems are not a part of the present invention per se., but rather are interfaced thereto, typically via small internal diameter hole containing flat sheet, or cone-shaped, skimmer containing interface means. It is also to be noted that the present invention utilizes the buffer gas as the ambient in which electric discharge production of random-spin electrons are produced, and that during operation said buffer gas pressure is nominally four-tenths (0.4) Torr and the total pressure in the single vacuum chamber contained essentially enclosed space is nominally pumped to, on the order of one-tenth (0.1) to thirty (30)Torr prior to entry of the buffer gas. The use of buffer gas as the electrical discharge media is a natural consequence of the preferred single chamber contained essentially enclosed space construction of the present invention system preferred embodiment. It is also noted that the single chamber contained essentially enclosed space, and particularly the means for entering said produced beam of predominately single handedness photons thereinto, (eg. a window which is essentially transparent to said predominately single handedness (electromagnetic radiation), photons), are, during use, heated by heating means to prevent condensation and deposition of the atoms therewithin which are pumped by said beam of predominately single handedness electromagnetic radiation photons. Acceptable windows are made from materials such as glass and quartz, and a nominal maintained temperature is disclosed as one-hundred-fifty (150) degrees Centigrade.
The present invention will be better understood by reference to the Detailed Description Section of this Disclosure, with appropriate reference being had to the Drawings.
It is therefore a primary purpose of the present invention to teach an optically pumped direct extraction electron spin filter system and method of utilizing a predominately single handedness, preferably laser system produced, beam of photons to optically pump electrons in atoms, (typically alkali atoms), to a dark-ground state wherein said electrons have a preferred-spin-polarization-direction. This is done in the presence of a magnetic field which is ideally co-linear with said beam of electromagnetic radiation photons; said system and method serving to, in a below atmospheric pressure ambient, convert a multiplicity of entered, typically electric discharge generated, electrons into a multiplicity of preferred-spin-polarization-direction electrons via optically pumped dark-ground state atom-electron exchange mechanism(s).
It is another purpose of the present invention to teach an optically pumped direct extraction electron spin filter system which comprises a single vacuum chamber containing enclosed space which is typically on the order of fifteen (15) centimeters long and four (4) centimeters in diameter, (ie. between one-hundred (100) and one-thousand (1000) cubic centimeters, and nominally approximately two-hundred (200) cubic centimeters volume).
It is a further purpose of the present invention to teach the use of xe2x80x9cbuffer gasxe2x80x9d which preferably comprises Helium as an electron preferred-polarization-direction yield enhancing means in an optically pumped, direct extraction, electron spin filter system.
It is a further purpose of the present invention to teach that said xe2x80x9cbuffer gasxe2x80x9d act as ambient for the electric discharge production of random-spin electrons which is caused to occur in said essentially enclosed space.
It is yet a further purpose of the present invention to teach use of a single essentially enclosed space xe2x80x9cvacuum chamberxe2x80x9d, in an optically pumped direct extraction electron spin filter system in which single essentially enclosed space xe2x80x9cvacuum chamberxe2x80x9d all required phenomena occur, to which are attached means for entering atoms, and means for effecting a below atmospheric pressure therewithin, and means for extracting electrons which have a preferred direction of spin, and means for effecting electron producing discharge therewithin.
It is a further purpose yet of the present invention to teach use of pressures on the order of one-tenth (0.1) to thirty (30) Torr in a single essentially enclosed space xe2x80x9cvacuum chamberxe2x80x9d in a an optically pumped direct extraction electron spin filter system, which pressures can be achieved by typical vacuum xe2x80x9croughingxe2x80x9d pumps alone.